(1) Field of the Invention
The present invention relates to a magnesia-based sintered body having a high density and excellent mechanical characteristics, and a process for the preparation thereof. More particularly, the present invention relates to a magnesia-based sintered body having a dense texture, a high hydration resistance and a high corrosion resistance, and a process for the preparation thereof.
(2) Description of the Related Art
Magnesia has a melting point as high as 2800.degree. C. and has an excellent corrosion resistance against an alkali metal or basic slag, and accordingly, it is thought that magnesia can be effectively used as a heat-resistant material for an alkali metal-melting crucible and the like. Magnesia, however, has an extremely poor hydration resistance, and further, a high-density magnesia sintered body generally used is often prepared by using a magnesia powder formed by thermal decomposition of a magnesium salt such as magnesium hydroxide or basic magnesium carbonate as the starting magnesia powder. This magnesia powder is difficult to sinter, and thus it is necessary to include various additives as the sintering aid at the sintering step. Moreover, in the magnesia powder formed by the thermal decomposition method, agglomerated particles are formed because of the remaining skeleton of the mother salt, and since these agglomerated particles remain even after mixing with the additive powder, a mixing at a level of primary particles is impossible, and thus the additive must be included in an amount much larger than the necessary amount.
As the means for overcoming these disadvantages, there has been proposed a method for obtaining a magnesia-based sintered body having a high hydration resistance and improved mechanical properties by adding magnesium phosphate, silica, zirconia or the like to the starting magnesia powder, but in the magnesia-based sintered body obtained according to the above-mentioned method, since the substance added is not uniformly present, an abnormal growth of particles occurs, and good results cannot be obtained with regard to the hydration resistance and corrosion resistance.